are unwilling to take responsibility for their own lives. they pay more effective tax than governor romney pays in his federal income tax. >> reporter: ryan went after president obama for his response to the u.s. consulate attack in libya. >> it took the president two weeks to acknowledge that this was a terrorist attack. >> reporter: while biden challenged ryan's proposed changes to medicare. >> you are jeopardizing the program. you're changing the program from a guaranteed benefit. >> reporter: it was a more heated back and forth than the first presidential debate. and biden often laughed at ryan's arguments. >> joe biden understood tonight he had to go back out there and do what president obama failed to do last week. >> reporter: with the race still tight for president obama and mitt romney, watched closely. >> i thought joe biden was terrific tonight. i couldn't be prouder of him. >> reporter: and in the end, the running mates shared a few laughs. >> i think the vice president very well knows that sometimes the words don't come out of your mouth the right way. >> i always say what i mean.